In support of this view he has devised the following extremely ingenious and remarkable experiment. A large Leyden jar, L, was arranged in such a manner that, while it received a steady charge from an electrical machine, it discharged itself, at intervals, across the air space at A, between two brass balls. The discharge had then two alternative paths before it; one through a conducting wire, C, the other across a second air space, between two brass balls at B. During the experiment, the two balls at A were kept at a fixed distance of one inch apart; but the distance between the two balls at B was varied. The conductor, C, used in the first instance, was a stout copper wire, about forty feet long, and having a resistance of only one-fortieth of an ohm. [Illustration: INDUCTION EFFECT OF LEYDEN JAR DISCHARGE. M Electrical Machine. L Leyden Jar. A B Air Spaces between Brass Knobs. C Conducting Wire.] It was found that, so long as the distance between the B knobs was less than 1.43 inches, all the discharges passed across between the knobs, in the form of a spark. When the distance exceeded 1.43 inches, all the discharges passed through the conductor, C, and no spark appeared between the balls at B. And when the distance was exactly 1.43 inches, the discharge sometimes took place between the knobs, and sometimes followed the conductor, C. The interpretation given to these facts is that the obstruction offered by the conductor C was about equal to the resistance of 1.43 inches of air; and it is proposed to call this distance, under the conditions of the experiment, the _critical distance_. Coming now to the application of these results, Professor Lodge argues that the conductor C, in his experiment, represents a lightning rod of unimpeachable excellence; and yet, in certain cases, the discharge refuses to follow the conductor, and prefers to leap across a considerable space of air, notwithstanding the enormous resistance it there encounters. In like manner, he says, a flash of lightning may, in certain cases, leave a lightning rod fitted up in the most orthodox manner, and force its way to earth through resisting masses of mason work and such chance conductors as may come across its path. This conclusion, he admits, is altogether at variance with the received views on the subject; but he contends that it is perfectly in accord with the scientific theory of an electrical discharge. The moment the discharge begins to pass in the conductor, it encounters the obstruction due to self-induction; and this obstruction is so great that the bad conductors offer, on the whole, an easier path to earth.